Sì, capisco che \greektext e \begin{otherlanguage}… fanno cose diverse.
Però considera questo esempio:
`\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
%\usepackage{textcomp}
\usepackage[utf8]{inputenc}
\usepackage[polutonikogreek,italian]{babel}
\usepackage[opticals,fullfamily]{MinionPro}
\input glyphtounicode
\pdfgentounicode=1
\usepackage{microtype}
\DeclareRobustCommand{\greektext}{%
\fontencoding{LGR}\fontfamily{MinionPro-OsF}\selectfont
\def\encodingdefault{LGR}
\begingroup\lccode`\~=`\'
\lowercase{\endgroup\edef~}{'}%
}
% kerning dell'apostrofo
\makeatletter
\catcode`\'=12
\def\qu@te{'}
\catcode`'=\active
\begingroup
\obeylines\obeyspaces%
\gdef\@resetactivechars{%
\def^^M{\@activechar@info{EOL}\space}%
\def {\@activechar@info{space}\space}%
}%
\endgroup
\providecommand\texorpdfstring[2]{#1}
\protected\def'{\texorpdfstring{\texqu@te}{\string'}}
\def\texqu@te{\relax
\ifmmode
\expandafter^\expandafter\bgroup\expandafter\prim@s
\else
\expandafter\futurelet\expandafter\@let@token\expandafter\qu@t@
\fi}
\def\qu@t@{%
\ifx'\@let@token
\qu@te\qu@te\expandafter\@gobble
\else
{}\qu@te{}\penalty\@M\hskip\expandafter\z@skip
\fi}
\scantokens\expandafter{%
\expandafter\def\expandafter\pr@m@s\expandafter{\pr@m@s}}
\makeatother
\begin{document}
{\greektext t`a >'onta s'wzein t`a fain'omena, `a 'a “i